A series of 1-naphthylmethylammonium n-alkanoates from acetate to triacontanoate produce isomorphic layered structures in the crystalline state. The interlayer distances, d-spacings, are proportional to the lengths of the alkyl chains. This is attributed to synergic intermolecular interactions; pi-pi and CH-pi interactions of the naphthalene rings between the cations, hydrophobic interactions of the alkyl chains, and two-dimensional hydrogen-bond networks between the primary ammonium cations and the carboxylate anions. Salts made from carboxylic acids wider than 5.5 A in the cross sections produce another columnar structure with a one-dimensional ladder-type hydrogen-bond network. Steric parameters of the acid components provide an explanation for the isomerism of the hydrogen-bond network.
The structure of methacrylate radicals and other related enolate
radicals with various
molecular sizes from small molecules to polymers was investigated by
ESR spectroscopy. The bromides
as precursors for the radicals were prepared by the reaction of the
corresponding alkenes with
bromotrichloromethane. The radicals were formed by
photoirradiation of a toluene solution of the
precursor in the presence of hexabutylditin at 213−318 K. The
polymer radicals were produced in the
ESR tube by the radical polymerization of the corresponding
methacrylate with an azo initiator in toluene
at 373 K or in p-xylene at 393 K. The ESR spectra of
the adduct radicals 1 was revealed to consist
of
binary components characterized by the following coupling constants and
g-values: a
1(3H) =
23.4−23.6
G, a
2(1H) = 21.6−22.3 G, and
g = 2.0043−2.0044 for conformation A and
a
1(3H) = 23.4−23.5 G and g
=
2.0043−2.0044 for conformation B. The α-nitrile radical
9, the dimer or trimer radicals 5−7,
and the
polymer radicals 8 also gave similar dual-conformation
spectra. On the basis of the coupling constants
determined for these spectra of the various enolate radicals, the
conformation model of the radicals was
discussed. It has been revealed that the pyramidalization of the
radical center and the A-strain-controlled
conformation due to the steric strain between the large substituents
account for the coupling constants
for the ESR spectra of the radicals. The propagation mechanism was
also discussed in relation to the
tacticity of the polymer.
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